1. Field of the Invention
This invention relates to the treatment of cellulosic fiber-containing fabric and articles made from such fabric with a cross-linking agent in the presence of a catalyst to improve durable press and shrinkage resistance properties of the fabric.
2. Discussion of Related Art
Treatment of cellulosic fibers (e.g., cotton, linen, hemp, rayon, etc.) and blends of fibers including cellulosic fibers with a cross-linking agent such as formaldehyde in the presence of moisture and a catalytic acid producer such as sulphur dioxide to improve the durable press (i.e., crease resistance) and shrinkage properties of fabric and articles made of such fibers is well documented in published literature and well known to those skilled in the art of fiber treatment. The physical chemistry of the process is also well documented and the effect of the cross-linking treatment on cellulosic containing fabric and articles of apparel made from such fabric has been researched and published extensively.
Exemplary prior art processes are described in the patent literature, where previous attempts have resulted in systems that are intended to solve some of the more practical problems of applying cross-linking treatment to finished articles of apparel in a low cost, high volume (i.e., commercial scale) and efficient manner, as well as cross-linking treatment systems generally for cellulosic material.
The problems intended to be solved by the prior art processes and systems are described in the various patents issued to inventors in this field, but this discussion is concerned with prior art systems for treating cellulosic and cellulosic blend fabrics that have been formed into finished articles of apparel on a high volume, continuous production basis to improve the durable press and shrinkage resistance properties of the apparel.
One approach to treating cellulosic fabrics and articles made from such fabrics described in the patent literature involves treating garments in a closed chamber using a gaseous cross-linking agent with steam and a gaseous catalyst, such as is described in U.S. Pat. Nos. 3,660,013 and 3,712,086 issued to G. Payet and J. Forg on May 2, 1972 and Jan. 23, 1973, respectively. This process involved the generation of gaseous phase cross-linking agent by heating powder of solid para-formaldehyde in a chamber containing the garments to be treated and then mixing the gas with steam and a gaseous cross-linking promoting catalyst such as sulphur dioxide in the chamber so that the mixture permeates the garments therein. The temperature in the chamber is then reduced for a period of time and the temperature in the chamber is then increased to the cross-linking temperature of the fabric and cross-linking agent. While successful, this process has drawbacks in that heated trays used to vaporize formaldehyde required constant cleaning and maintenance, the moisture content of the fabric, while critical, was difficult to control, and excess formaldehyde absorbed into the fabric weakened the fabric and required careful cleaning of residual, non-cross-linked formaldehyde from the garments after the cross-linking procedure to avoid undesirable formaldehyde odors and irritant being left on the garments.
In U.S. Pat. No. 3,837,799 issued to K. W. Wilson, R. Swidler and J. P. Gamarra on Sep. 24, 1974, a process is described for crease proofing garments made from cellulosic fiber-containing fabric using gaseous formaldehyde generated by heating para-formaldehyde in mineral oil and subjecting cellulosic fiber-containing fabric with previously applied latent catalyst to the gaseous formaldehyde in a reaction chamber at about 90.degree.-150.degree. C. In this process, two controlled procedures are required to expose the fabric to catalyst and formaldehyde, the process is both temperature and moisture sensitive, and careful cleaning of the formaldehyde and water soluble catalyst from the fabric is required.
U.S. Pat. Nos. 3,960,482 and 3,960,483 issued to G. L. Payet on Jun. 1, 1976 describe a durable press process involving a similar procedure for pre-conditioning fabric with a water soluble catalyst and then subjecting it to formaldehyde vapors and moisture before curing (cross-linking) the fabric and formaldehyde at cross-linking temperatures. The problems of the prior art systems are discussed in this patent, particularly the difficulties encountered in precisely controlling moisture content in the fabric in the presence of a toxic gas and a gaseous catalyst. In accordance with the process described in this patent, the moisture content of the cellulosic fibers is controlled so they have over 20% weight of moisture and contain a selected amount of catalyst when exposed to cross-linking formaldehyde vapor. This enables the process to be carried out at a lower temperature (i.e., room temperature) with a drastically reduced concentration of formaldehyde (6% by volume) as compared with prior art procedures. This process, as with processes previously used, required separate moisture, formaldehyde and catalyst applications to the fabric, and also was highly dependent on the moisture content of the fabric for its successful implementation. The moisture was introduced into the fabric as a spray, mist or fog, or was padded on the fabric alone or with a catalyst. This left the problem of generating the gaseous cross-linking agent and applying it to the fabric in a uniform manner as rapidly as possible. Presumably, the cross-linking formaldehyde vapor used in accordance with the process described in the patent was generated from vaporizing solid form para-formaldehyde, which entailed maintenance problems already discussed above.
U.S. Pat. No. 3,865,545 issued to J. H. Forg and G. L. Payet describes an other process for treating cellulosic fiber articles to impart a durable press thereto involving vaporizing solid para-formaldehyde in a reaction chamber and exposing the fabric articles to the formaldehyde vapors, steam and gaseous catalyst for a period of time at a temperature initially ranging from 120.degree. F. to about 145.degree. F., followed by cooling the fabric 10.degree.-30.degree. by the time of completion of the procedure. Steam and free chemicals are then purged from the chamber before the temperature in the chamber is increased to cross-linking temperature. Steam and fresh air are then circulated over the articles to clean them of residual odors. As in previously described processes, control over moisture content, cross-linking agent concentration and catalyst content in the fabric as well as temperatures are all critical to some degree; vaporization of solid para-formaldehyde is difficult to control precisely; and the formaldehyde vapor generating system is maintenance intensive.
A process for the continuous treatment of continuous fabric and/or garments for improved durable press characteristics is described in U.S. Pat. No. 3,884,632 issued to G. L. Payet and B. D. Brummet on May 20, 1975. In this patented system, the material to be treated was advanced through successive treating stations where it was sequentially moisturized, subjected to formaldehyde (generated by vaporizing solid para-formaldehyde) and catalyst, heated and cross-linked, and cleaned in a continuous process.
U.S. Pat. No. 4,032,294 issued Jun. 28, 1977 to R. D. Thompson, D. Thompson and M. A. Beeley describes a similar process for continuously treating garments using a series of workstations and chambers to process equal sized batches of garments.
U.S. Pat. No. 3,706,526 issued on Dec. 19, 1972 to R. Swidler and K. Wilson describes a durable press process using formaldehyde and sulphur dioxide to treat cellulosic fabrics. Moisture content of the fabric is described as being very important to achieve a self-limiting reaction (cross-linking) but moisture, gaseous formaldehyde and gaseous catalyst are all conveyed to the fabric by different routes and equipment, therefore requiring careful control over the system at all times to maintain proper proportioning of chemicals and moisture reaching the fabric.
U.S. Pat. No. 4,067,688 issued on Jan. 10, 1978 to G. L. Payet describes a durable press process for cellulosic fiber-containing fabrics using formaldehyde vapor and a liquid catalyst (aryl sulfonic liquid or acid) in a high moisture environment. The moisture, formaldehyde and catalyst generally are introduced to the fabric via different routes in the process, requiring careful control over operating parameters.
A known commercial process involves direct injection of a known quantity of liquid formaldehyde cross-linking agent into a stream of steam supplied at a temperature sufficient to vaporize the formaldehyde and then supplying a quantity of the steam with entrained vaporized formaldehyde into a treating chamber wherein a cellulosic containing fabric article has been placed for treatment. A gaseous cross-linking promoting catalyst such as sulfur dioxide is then introduced into the chamber and the fabric article is exposed to the mixture of steam, formaldehyde, and sulfur dioxide for a preselected time. The free steam, formaldehyde and sulfur dioxide (not retained by the fabric article) are then purged from the treating chamber and the chamber's temperature is elevated to cross-linking temperature for a sufficient time to cross-link the cellulosic material in the fabric, following which the chamber is cooled and the fabric is removed from the chamber. This process, while facilitating the delivery of formaldehyde to the fabric article to be treated by using a stream of steam as a vehicle, still required close control over the supply of gaseous catalyst, along with all of the gaseous supply tanks, conduits, valves and controls associated with the sulfur dioxide supply system. Inside the treating chamber, the gaseous catalyst moved independently of the steam and vaporized formaldehyde, so experimentation was required to ensure that the appropriate amount of sulfur dioxide gas actually reached the fabric with the cross-linking formaldehyde in a correct manner to ensure good cross-linking results for the particular fabric undergoing treatment. Achieving minimum strength loss in the treated fabric article and low residual free chemicals to be removed from the fabric after completion of the cross-linking process required careful control over the process.
Thus, while the known systems for cross-linking cellulosic containing fabric articles using steam, cross-linking agent and cross-linking promoting catalyst in a treating chamber have achieved some success, problems still remain in terms of processing cost, speed and efficiency, as well as residual chemicals left in the cross-linked fabric. Fabric strength loss resulting from cross-linking and achievement of shrinkage control with acceptable durable press quality remained to be achieved at minimum cost.